1. Field of The Invention
Apparatuses and methods consistent with the present invention relate to a data transmission in a wireless relay system. More particularly, the present invention relates to a method of selecting an optimal transmission mode based on a channel capacity of an individual link that is measured by a mobile station.
2. Description of Related Art
Multiple In Multiple Out (MIMO) technology is currently being discussed in association with improving a performance of a mobile communication system. The MIMO technology designates a technology which installs a plurality of antennas in each of a base station (BS) and a mobile station (MS), and increases a high speed data service coverage area with high throughput around the BS.
In a MIMO system, a data transmission rate (hereinafter, data rate) increases in proportion to a minimum value of a number of transceiving antennas. However, since a plurality of antennas cannot be installed in the MS due to a spatial restriction, there are some constraints to acquire an overall high multiplexing gain.
Accordingly, a wireless relay technology which can reduce a transmission loss and improve a multiplexing gain by directly transmitting data to an MS and also transmitting the data via at least one relay station (RS), is required.
FIG. 1 is a diagram illustrating a configuration of a wireless relay system according to a conventional art. Referring to FIG. 1, the wireless relay system includes a BS 10, at least one RS 20, and an MS 30. Here, the BS 10 provides a wireless communication area to an individual cell 100. The RS 20 intermediates data to be transmitted/received between the BS 10 and the MS 30. Also, the MS 30 wirelessly transmits/receives the data with the BS 10.
As shown in FIG. 1, in the wireless relay system, when transmitting data from the BS 10 to the MS 30, the data may be directly transmitted via a BS-MS link 12. Also, at the same time, the data may be transmitted via a BS-RS link 11 and an RS-MS link 21. As described above, in the wireless relay system, a multiplexing gain may be acquired by installing the RS 20 in a particular location of the cell 100 and increasing a number of data transmission paths between the BS 10 and the MS 30.
FIG. 2 illustrates operations based on two types of protocols associated with data transmission in a wireless relay system, according to the conventional art. Here, the protocols have been discussed in a number of papers including Nabar and Bölcskei, “Space-time signal design for fading relay channels” (2003); Nabar, Bölcskei, and Kneubuhler, “Fading relay channel: performance limits and space-time signal design” (2004); Hasna and Alouini, “Optimal power allocation for relayed transmissions over Rayleigh-fading channels” (2004); Laneman, Tse, and Wornell, “Cooperative diversity in wireless networks” (2004), Deng and Haimovich, “Power allocation for cooperative relaying in wireless networks” (2005); Larsson and Cao, “Collaborative transmit diversity with adaptive radio resource and power allocation” (2005); and the like.
According to a protocol (protocol 1) 210, the BS 10 simultaneously transmits data to the RS 20 and MS 30 in a first time slot 211. Thus, the MS 30 receives the data from the BS 10 in the first time slot 211. The RS 20 forwards the data received from the BS 10 to the MS 30 in a second time slot 212.
Conversely, according to another protocol (protocol 2) 220, the BS 10 transmits data to only the RS 20 in a first time slot 221, and transmits the data to only the MS 30 in a second time slot 222. The RS 20 forwards the data, received from the BS 10, to the MS 30 in the second time slot 222. Thus, the MS 30 simultaneously receives the data from the BS 10 and the RS 20 in the second time slot 222.
As described above, in the wireless relay system according to the protocol 210, since the MS 30 receives the data a number of different times, the protocol 210 may be regarded as a Single Input Multiple Output (SIMO) method. Conversely, in the wireless relay system according to the protocol 220, since the MS 30 simultaneously receives data from a plurality of channels, the protocol 220 may be regarded as a Multiple Input Single Output (MISO) method.
Conventionally, a method of acquiring a diversity gain based on the protocol 210 is utilized due to easy analysis. Such is the case in the above-mentioned papers. Here, in the protocol 210, algorithms are developed in a form of the SIMO method. Thus, to increase throughput, i.e. a cell capacity based on the protocol 210, only a limited method, such as a power control method or a path selection method, may be utilized.
Also, some studies, which are based on the protocol 220 and usually focus only on how to increase a diversity gain, do not address a way to improve throughput.
Accordingly, an aspect of the present invention suggests a wireless relay technology which can outperform the above-described conventional art and also can increase a cell capacity and expand a cell radius based on the protocol 220.